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CS1 Python Subgoals

Section 7.1 Use Math

Subgoals for using libraries:.

  1. Import module or function (if needed)
    1. With alias (optional)
  2. Determine whether parameters are appropriate for function
    1. Number of parameters passed must match function documentation
    2. Type of parameters passes must match function documentation
  3. Determine what the function will return (i.e., data type), print, and/or change state of arguments and where it will be stored (nowhere, somewhere)
  4. Evaluate expression as necessary

Subsection 7.1.1

Problem:
Given the following code:
a_number = int(input("What number do you want to know the length of?"))
Use the log10 function of the built-in math library to calculate the number of digits in a number taken from the user.

Subsection 7.1.2 1. Import module or function (if needed)

First, we need to import the desired library, which is named math. We do not need to alias the name because math is already short and descriptive.
import math

Subsection 7.1.3 2. Determine whether parameters are appropriate for function

According to the documentation, the log10 function consumes x, which is an integer.
That integer is the value we will get from the user.
math.log10(a_number)

Subsection 7.1.4 3. Determine what the function will return (i.e., data type), print, and/or change state of arguments and where it will be stored (nowhere, somewhere)

The function will return the base-10 logarithm of X, which will tell us the number of digits required. Since we need to print the result, we’ll need to store the function call’s result in a variable digits.
digits = math.log10(a_number)

Subsection 7.1.5 4. Evaluate expression as necessary

We then finish the program by printing:
print(digits)
Answer.
The completed program:
import math

a_number = int(input("What number do you want to know the length of?"))
digits = math.log10(a_number)
print(digits)
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